The present invention relates to pellets comprising fibers impregnated with resin. The pellets incorporate a mixed lubricant sizing composition comprising at least one cationic lubricant and at least one non-ionic lubricant. These pellets may be consolidated to form fiber reinforced resin composites.
Fibrous strands comprising a plurality of individual fiber filaments have been used, both in continuous or chopped form, to impart improved material properties to reinforced composites such as tensile strength, percent elongation, flexural modulus, impact strength, and deflection temperature under load. Reinforced composites are useful in various applications such as injection moldable automotive parts.
One method of making reinforced composites is by mixing fibrous strand choppings, usually glass strand choppings, with a molten synthetic resin in an extruder and injecting the mixture into a mold. A major draw back to this method is the high shear stress placed on the fibers of the chopped strand causing the fibers to be comminuted into shorter segments. These shortened fibers impart reduced material properties to a reinforced composite when compared to longer fibers.
An alternative to the direct mixing of chopped strand with synthetic resins involves drawing a grass strand though an die to impregnate a continuous strand with a polyolefin resin. The impregnated strand may then be chopped into pellets. These pellets may be used by themselves or mixed with additional resin to make a reinforced composite. In either case, this method greatly reduces or eliminates the shortening of glass fibers and yields composites with more desirable properties. Unfortunately, this method does impart some physical stress to the fiber strand.
Undesirable physical damage such as fracture may be done to the individual filaments which make up a strand as the strand is pulled through an impregnation, die. Additionally, filament fracture may also occur as the strand is usually drawn over a breaker bar which splays the individually fibers to increase the amount of resin which may be impregnated on the strand. This fracture or breakage of the individual filaments leads to a frayed or fuzzy looking strand surface and is often referred to xe2x80x9cfuzzing.xe2x80x9d
Fuzzing is the result of abrasion of the strand as it is drawn over the breaker bar or through the impregnation die. Not only does fuzzing lead to undesirable properties in a reinforced polyolefin composite, fuzzing may also cause the impregnation die to become clogged causing undesirable interruptions during manufacture. Fuzzing also limits the speed at which impregnated stands can be manufacture because as the strand is drawn across the breaker bar and impregnation die at faster speeds the likelihood of fuzzing increases. Fuzzing also appears to propagate additional filament fracture leading to additional fuzzing and the complete fracture of the strand.
Several lubricants have been used in sizing compositions to reduce fuzzing. Unfortunately, high levels of lubricants are often needed to reduce fuzzing. When the ultimate use of a sized strand is to reinforce a synthetic resin, lubricants are often incompatible with the resin and therefore lubricant content should be minimized as mush as possible. Accordingly, it would be desirable to discover a sizing wherein the amount of lubricants is minimized.
It has now surprisingly found that a mixed lubricant system comprising at least one cationic lubricant and at least one non-ionic lubricant greatly reduces fuzzing. Additionally, it has been found that a cationic lubricant and a non-ionic lubricant work in synergy to reduce fuzzing. Furthermore, it has been found that because of the synergistic relationship, the amount of lubricant present in a sizing may be minimized while still reducing or preventing fuzzing. The present invention is particularly useful in the manufacture of impregnated strands because the impregnation process involves many points of abrasive contact and a higher potential for fuzzing.
An object of the present invention is a sizing composition useful to prevent fuzzing comprising a cationic lubricant and a non-ionic lubricant and is hereafter referred to as xe2x80x9cmixed lubricant sizing.xe2x80x9d
Another object of the invention is a strand which incorporates the mixed lubricant sizing and is hereafter referred to as xe2x80x9cmixed lubricant strand.xe2x80x9d The mixed lubricant strand is preferably made by the application of the mixed lubricant sizing to a plurality of individual fiber filaments which are then gathered into a strand.
Another object of the invention are pellets which incorporate the mixed lubricant sizing and is hereafter referred to as xe2x80x9cmixed lubricant pelletsxe2x80x9d The mixed lubricant pellets are preferably made by impregnating the mixed lubricant strand with a synthetic resin, cooling to form an impregnated strand, and chopping the impregnated strand to form the mixed lubricant pellets.
Yet another object of the invention is a reinforced resin composite incorporating the mixed lubricant sizing and is hereafter referred to as xe2x80x9cmixed lubricant composite.xe2x80x9d The mixed lubricant composite comprises a fiber reinforcing material dispersed in a synthetic resin matrix. The mixed lubricant composite is preferably made by directly consolidating the mixed lubricant pellets.